System and apparatus for inspecting elongated welds

ABSTRACT

An ultrasonic inspection system is disclosed for inspecting an elongated weld, such as the long seam weld on pipe. Longitudinal wave ultrasonic transducers are provided for inspecting along the thickest portion of the weld and along the plate adjacent to the weld, and shear wave ultrasonic transducers are provided for inspecting the boundary zones between the weld metal and plate being welded. Electronic pulsing and signal processing apparatus is provided for providing drive to a data recorder on which separate graphical representations of the condition of the weld, of the condition of the plate adjacent the weld, and of the boundary zones of the weld are simultaneously provided. The transducers are mounted on an inspection head which is in turn mounted on a carriage which may be inserted into racked pipe for inspecting the long seam weld. The inspection head includes guide means, such as rollers, for guiding the head along the long seam weld of the pipe. The inspection head is resiliently urged against the inside wall of the pipe and counterweights are provided for balancing the inspection head in the position required for inspection so that the seam may be inspected when the pipe is at any rotational orientation.

1"; J y I xa 3,568,847 1 United DIHIES I A I i- N l 1 3,868,847

\ n 1:, r Gunkel K 7 A 1 Mar. 4, 1975 1 SYSTEM AND APPARATUS FOR 1571 ABSTRACT INSPECTING ELONGATED WELDS An ultrasonic inspection system is disclosed for in- [76] lnventor: Walter A. Gunkel, 6515 Moss Oak. Spectlng g lgrc fll iilda as the long Seam San Antonio 7 7 weld on pipe. Longitudinal wave ultrasonic transducers are provided for inspecting along the thickest por- [22] Fled: 1972 tion of the weld and along the plate adjacent to the 2 1 App] 31 300 weld, and shear wave ultrasonic transducers are provided for inspecting the boundary zones between the weld metal and plate being welded. Electronic pulsing (52] US. Cl. 73/67.8 S and Signal processing apparatus is provided for provid [51] Illl. Cl. G01" 29/04 ing drive to a data l.ecordm. on which saparate graphi [58] Field Of sealCh 73/675, 67.6, 67.7, 67.8,

cal representations of the condition of the weld, of the condition of the plate adjacent the weld, and of the boundary zones of the weld are simultaneously prolsfl References cued vided. The transducers are mounted on an inspection UNlTED STATES PATENTS head which is in turn mounted on a carriage which 73/679, 67.5 R. 67.8 R, 67.8 S

3350925 ll/l967 Coy 73/ ,7 g 5 may be inserted into racked pipe for inspecting the 3.455.150 7/1969 Wood 73/678 5 long seam weld. The inspection head includes guide 3.540266 11/1970 Lol grcn 73/678 5 means, such as rollers, for guiding the head along the 3,575,044 4/l97l r long ean weld of [he The ins ection head is re- 3.79l.l99 2/l974 Toth et al 73/679 siliently urged against the inside wall of the pipe and counterweights are provided for balancing the inspection head in the position required for inspection so that the seam may be inspected when the pipe is at any rotational orientation.

Primary Examiner-Richard C. Queisser Assistant Etaminew-Stephen A. Kreitman Attorney, Agent, or FirmW. F. Hyer; Marvin B. Eickenroht 12 Claims, 21 Drawing Figures are a 448 MA 32 43A 29 PATLNTLOHA 3.868.847

SHEET 5 er 4 Q 1 1 L A L L CLOCK E] r r r m- SHEAR BANG E L-WAVE BANG 2 T Y r BLANK/N6 PULSE ECHO SIGNALS FIG. 75

CRYSTAL L WA VE VOLTAGE/ SHEAR CRYSTAL VOLTAGE 76 [\MA/N BANG (SHEAR AT 7.6 MC, L-WAVE AT 800 KC) ./NSPECT/ON PER/OD 500 ,u s /MA/N BANG ec )LA/N BANG L- WAVE 1, AN

L R ECHO FROM NORMAL \NALL REDUCED ECHO FROM OEFECT OR TH/N WALL WALE fH/CKNESS F G. 7 7

I 72- 75/Js-L NORMA L WALL THICKNESS ECIHO (DEFECT PRESENCE) .--250ms ---J MA/N BANG EM 500 ms /POS/T/ON ALONG WELO /50A T NORMAL SLAG 7 THICKNESS WELD 53B 530w :6OOm/53A REDUCED 530 L g WELD THICKNESS L g .L 5 i 62 CRACK IN BOUNDARY THIN WALL ZONE (PROP. TO

y OEFECT S/ZE 400ml NORMAL PLATE THICKNESS PLATE LAM/NAT/ON FIG. 18

specting the long seam weld of a pipe, particularly when racked.

Adequate inspection of pipe requires that the long seam weld be inspected. In large pipe it is desirable to do this while the pipe is racked in order to avoid pipe handling which requires expensive equipment, is time consuming, and frequently damages the pipe. However, when racked, the individual pipe lengths will generally be at different rotational orientations and the prior art does not provide practical inspection apparatus which will inspect along the long seam weld requiring some orientation and handling of the pipe. Also, even when pipe is laid out on the ground in an unracked condition, prior art inspection devices that inspect along the outside of the long seam weld generally require some rotating of the pipe for orientation of the weld. Furthermore, it is desirable that the inspection apparatus used be lightweight and portable and that it be capable of operation by as small a crew as possible.

Also, in the past, ultrasonic inspection of the welds has generally been provided by scattering or speading ultrasonic pulses generally through the weld and noting the arrival of echo pulses in a defective weld as opposed to a good weld. In some prior systems longitudinal wave inspection is provided for, and in others shear or transverse wave inspection is provided for. In one such system, ultrasonic shear wave pulses are sent through the plate adjacent the weld and on each side ofthe weld, at a propagation angle in the plate ofabout 80 so that a spead beam of pulses is provided into the weld. The same ultrasonic signals are used to inspect the boundary zones of the weld, the heart of the weld and throughout its thickness, and the plate adjacent the weld. See Krautkramer, Ultrasonic Testing of Materials, Springer-Verday, New York, 1969. However, such a system provides relatively poor selectivity, sensitivity and signal to noise ratio, particularly as the beam is spead out to cover more area, and may miss defects in the heart of the weld. Also, the type of readout provided by such a system requires interpretation by an operator of considerable skill in pipe inspection in order to determine the type and severity of a defect located, and its exact location.

It is thus an object of this invention to provide apparatus for inspecting the long seam weld of pipe at any orientation of the weld being inspected.

Another object of this invention is to provide such apparatus which is lightweight and portable and particularly adaptable to inspecting the long seam weld of racked pipe, thereby eliminating pipe handling, providing independence of yard activity, etc.

Another object of this invention is to provide such apparatus which may be placed in the pipe and about the weld being inspected, so that the apparatus can propel itself along the weld and accomplish its inspection function automatically.

Another object of this invention is to provide such apparatus for use in an ultrasonic inspection system which permits simultaneous longitudinal and transverse inspection of the weld with the same apparatus and with synchronism between the two types of weld inspection provided for, to provide better and overlapping inspections of the weld and weld areas.

Another object of this invention is to provide such apparatus that is particularly adaptable for use in ultrasonic inspection of an elongated weld, such as along the inside or outside of the long seam weld of pipe or the W El 4-... t

Another object of this invention is to provide an ultrasonic inspection system, and apparatus therefore, for inspecting elongated welds with better selectivity, sensitivity, signal to noise ratio, and reliability then provided by prior such systems.

Another object of this invention is to provide such a system and apparatus in which root or cap cracks and other defects in the boundary zone of the weld, defects in the plate adjacent to the weld, and defects in the heart of the weld can be reliably detected and readily distinguished from each other by techniques specially designed individually to provide maximum effectiveness in these areas of the weld structure and to do so by persons of lesser skill in the pipe inspection art than heretofore required.

Another object of this invention is to provide such a system and apparatus which is sensitive to and provides an indication of the porosity in the weld, the various defects of the weld, such as burn through, and of the presence of cracks, slag inclusion, voids and poor fusion of the weld, and offset plate.

Another object of this invention is to provide a relatively easily read and understandable composite, permanent record on a single recording medium of the condition of the weld, the condition of the boundary zone of the weld, and the condition of the plate adjacent the weld.

These and other objects of this invention, which will be apparent upon consideration of the appended claims and drawings, and the detailed description to follow, are accomplished in accordance with the preferred embodiments of this invention disclosed by providing a carriage that can propel itself along the inside of a pipe being inspected and support a rotatable shaft along the axis of the pipe. An inspection head may be rotatably and resiliently mounted on an arm extending from the shaft so that it may be rotated to any position about the circumference of the pipe corresponding to the orientation of the weld, and resiliently urged against the inside weld of the pipe about the weld. Guide means are provided on the inspection head for guiding the inspection head along the weld as the carriage moves throughout the pipe. A counterweight may also be provided to substantially balance the inspection head at its position on the circumference of the pipe, and the inspection head may be mounted on and balance about the arm extending from the shaft by an universal coupling so that it can float and ride along the weld and adjust to irregularities in the weld or the inner wall of the pipe. A second counterweight may also be provided to help balance the inspection head on the arm supporting II.

The inspection head includes at least one inspection transducer, which is preferably an ultrasonic transducer, which may be mounted in the inspection head with a floating relationship so that it also adapts to the irregularities in the surface of the weld or pipe wall. Means may also be provided for maintaining a fluid coupling and bearing surface between the transducer and the weld or pipe wall.

The apparatus described may be used in a system for inspecting elongated welds which includes, on the inspection head, a first ultrasonic transducer which rides along the weld to specifically inspect into the heart of the weld (and through its thickness); a plurality of second transducers arranged along the inspection head and specifically orientated to have substantially their maximum signal sensitivity in response to defects, such as cracks in the boundary zones of the weld (said boundary zones of the weld being defined as the zone of the junctions of the weld with the plate being welded); and third ultrasonic transducers for specifically inspecting plate adjacent the weld. This arrangement can provide for simultaneous longitudinal wave and transverse or shear wave inspection of the weld with overlapping coverage, so that the first and third transducers are longitudinal wave transducers and the second transducers are shear wave transducers. Suitable pulsing and signal processing electronics is provided for pulsing the transmitting elements of the respective transducers and processing echo signals received by the transducers. Output signals from the electronics may be utilized to drive a chart recorder which will simultaneously display a first indication of the thickness (or of the presence of a defect) of the heart of the weld; a second indication of the presence or lack or presence of a crack in one or more of the weld boundary zones; and a third indication of the thickness (or presence ofa defect) in the plate adjacent the weld.

Since each of the transducers mentioned can be specifically oriented and adjusted for its specific inspection application a spread beam is not required and better selectivity, sensitivity, signal to noise ratio and reliability can be provided over prior ultrasonic weld inspection systems. For example, better sensitivity can be provided in steel with an ultrasonic beam travelling through it with a propagation angle of about 45 with respect to the plate surface, and the shear transducers for inspecting each boundary zone can be adjusted to provide such a beam which is focused on the particular boundary zone to be inspected for maximum response to a crack or other defect in the respective zone. Also, by use of the separate transducers for inspecting different parts of the weld (and the adjacent plate) distinctive readouts of the condition of each part of the weld and adjacent plate being inspected can be provided which yields useful defect discrimination information and can be easily read and understood by persons of lesser skill in pipe inspection than the readouts of prior systems.

The inspection head can be mounted on a carriage for movement through the interior of a pipe (including racked pipe) to inspect the long seam weld of the pipe,

'. or moved along the long seam weld on the outside of the pipe. Also, the features of this invention may be employed in other inspection apparatus for inspecting elongated welds between two plates, girth welds between pipe, and the like.

In the drawings, wherein like reference numerals are used throughout to designate like parts and wherein preferred embodiments of this invention are illustrated;

FIG. 1 is a perspective view of the preferred form of inspection apparatus of this invention, prior to insertion into a pipe being inspected;

FIG. 2 is an end 'view of the inspection apparatus of FIG. 1, shown inside a pipe being inspected;

FIG. 2A is an enlarged view at 2A in FIG. 2 showing details ofa typical double submerged arc weld between two plates;

FIG. 3 is a top view of the inspection head of the FIG. 1 apparatus shown in a pipe, and with the pipe partially cut away;

FIG. 4 is an enlarged end view of the inspection head of the FIG. 1 apparatus shown in the pipe;

FIG. 5 is a side view in elevation of the inspection head of the FIG. 1 apparatus;

FIG. 6 is a longitudinal sectional view of the inspection head of FIG. 1;

FIG. 7 is a sectional view taken at 7-7 in FIG. 6;

FIG. 8A is a perspective view of an alternate form of the mounting of inspection head of the rotating shaft permitting retraction of the inspection head when inserted into a pipe;

FIG. 8B is an end view in elevation of another form of guide means for adjusfing the position of the guide rollers;

FIG. 8C is a top view of the guide means of FIG. 88;

FIG. 9 is a top view of the preferred form of inspection head of the apparatus of FIG. I showing the details of the arrangement of thetransducers in the inspection system of this invention;

FIG. 10 is a sectional view taken at 10-10 in FIG. 6 with a partial cut away;

FIG. 11 is a cross sectional representation of the relationship of the transducers of the FIG. 8 inspection head, and a weld and adjacent plate being inspected;

FIG. 12 is an overall schematic of the preferred arrangement of the transducers, pulsing and signal processing electronics, and a chart recorder of the system of this invention;

FIG. 13 is a more detailed schematic of a time base measuring circuit utilized in the FIG. 12 circuit;

FIG. 14 is a more detailed schematic of the electronics of FIG. 12;

FIG. 15 is a wave form chart applicable to the signal outputs of the FIG. 14 electronics;

FIG. I6 is a wave form chart illustrating the operation of the pulser electronics;

FIG. 17 is a wave form chart showing the relationship of the main bang transmitted signals and the echo signals at the transducers; and

FIG. 18 is a pictorial representation ofa typical chart recorder readout obtained by use of the present inven- IIOII.

Referring to the drawings, in FIG. I the preferred form of pipe inspection apparatus of this invention, such as used for inspecting racked pipe, is illustrated by the numeral 10 as including a tubular sleeve II in which a rotatable shaft 12 is mounted. Sleeve 11 and shaft 12 may be supported along the axis of a pipe being inspected, such as a pipe P having a long seam weld W as shown in FIG. 2, by six legs 13, three located at each end of sleeve 11 and mounted apart. Each of legs 13 include wheel 13a and may be made of telescoping threaded members (the threads not being shown in FIGS. 1 and 2) which can be adjusted in length by screwing one of the members into the other, so that the carriage can be mounted in pipes of different diameter with shaft 12 substantially along the axis of the pipe. As shown, a sprocket I4 is provided on one of wheels 13a and it may be connected by a belt to a drive motor M (two motors may be used, if desired) which may be battery powered. Of course, other arrangements of the carriage may be provided for supporting rotary shaft 12. Apparatus can be made of aluminum so that it is lightweight and portable and can be easily handled by a two man crew.

As shown in FIGS. 1 and 2 an inspection head is supported for rotation by shaft 12. A hub 16 is mounted on shaft 12 and supports a pair of spaced apart, parallel support members 17 and 18 extending perpendicular to the axis of rotation of shaft 12, and an arm 16A extending radially away from members 17 and 18. Inspection head 15 is mounted on one end of an arm 19 as hereinafter explained in detail, which is pivotally mounted by a pin 20 on and between members 17 and 18. Inspection head 15 is preferably balanced about its mounting on arm 19 and a counterweight 21 is mounted on the other end of arm 19 to counterbalance the weight of inspection head 15 on arm 19, and this end of arm 19 is connected by a spring 22 to a spacer block 23 (FIG. 6) mounted between arms 17 and 18. Inspection head 15 is thus resiliently mounted on shaft 12 and spring 22 provides a force urging inspection head 15 against the inner wall of pipe P so that as carriage 10 moves along the pipe inspection head 15 will move along and against the wall. Another counterweight 165 (which may be adjusted up and down arm 16A by a set screw) is provided on the end of arm 16A so that arm 16A and members 17 and 18, and their attachments can be balanced on shaft 12 at any rotational orientation.

However, the tension of spring 22 should be such that as inspection head moves along the inner wall of pipe P, it can move away from the wall when irregularities in the surface are encountered, otherwise it may bind against the wall or inspection transducers may be damaged.

The preferred form of inspection head 15 illustrated includes two flat aluminum plates 24 and 25 mounted on end blocks 26 and 27 which are sloped to confrom to the curved inner wall of pipe P. Small, thin nylon strips 24A and 25A may be mounted on the outer edges of plates 24 and 25 to serve as runners and space the plates from the surface of the pipe. The ends of plates 24 and 25 at the center of inspection head 15 are spaced apart to form an elongated slot 28 into which a portion ofweld W will extend when the inspection head is placed over the weld, slot 28 being wide enough so that it clears the weld by a small amount as shown in FIG. 4, so that the edges of plates 24 and 25 adjacent weld W generally will not rub against the weld. Also mounted on end plates 26 and 27 and extending from each of inspection head 15, are water pipes 29 and two roller support plates 30. Water pipes 29 are connected as hereafter explained to a source of water for lubricating the surface of pipe P ahead of inspection head 15 in either direction, and to provide an acoustic fluid coupling and bearing surface for each of the transducers of head 15.

In order to aid placing inspection head 15 in and taking it from a pipe, a retracting mechanism such as shown in FIG. 8A may be provided which lowers the head. In this case. plates 17 and 18 are replaced by an arm including telescoping members 17A and 17B and a, for example. set screw 18A in a slot in member 17A which permits the position of member 1713 inside of 17A to be adjusted and set. If desired. a lever mechanism (not shown) may be provided for moving member scribed, as well as the arrangement of the transducers,

178 in member 17A from a retracted position for head 15, to a raised position for head 15 for inspection.

Two rollers 31 are mounted on each of support plates 30 so that when head 15 is in position about weld W, and the weld is along slots 28, one such roller is along an edge or side of weld W (see FIG. 4) at each end of head 15, to function as guide means for guiding inspection head along weld W and maintaining the proper orientation ofthe inspection head transducers to the weld. Of course, other forms of guide means may be provided, for example, nylon or teflon bearing pads could be mounted on plates 24 and 25 on each side of slot 28 to rub against weld W. However, the roller arrangement described is preferred since it provides smoother operation and less force is required to move head 15 along the weld.

In order to permit adjustment of the guide rollers for different sizes of weld beads, the arrangement better shown in FIGS. 88 and 8C is preferred, the latter FIG. showing only one side of the guide means in detail since it is symmetrical. In this arrangement plate 30 is mounted through slotted openings 30A to permit the vertical position of rollers 31 to be adjusted. Also, rollers 31 are mounted through a slotted opening 31A in the top of plate 30 to permit adjustment of rollers 31 towards and away from weld W. A threaded set screw 318 may be provided for adjusting the position of a plate 31C to which roller 31 is secured. so that plate 31C moves with respect to plate 30 in the direction noted by the arrow in FIG. 8B. When the position of the rollers 31 is set along the weld bead, a set screw 318 may be pinned by a pin passing through it to avoid displacement. When the rollers 31 are properly set, all of head 15 (including pads 24A and 25A) except the transducers will ride off of the pipes wall with a small clearance unless an out of round portion is encountered. Of course. this arrangement of guide means deon a suitable inspection head could also be used to inspect a girth weld.

The details of the counting of inspection head 15 on arm 19 is shown in FIGS. 4, 5, 6, and 7. Arm 19 includes a plate 19A extending at right angle to arm 19 and mounted on the end opposite the end that counterweight 21 is mounted on. A universal coupling 32 including a swivel connector 32A (see FIG. 7) is mounted on plate 19A and inspection head 15 is mounted on coupling 32 to permit universal movement of inspectin head 15. As shown in FIG. 6 inspection head 15 includes two plastic water manifold blocks 33 and 34 mounted on the lower side of plates 24 and 25 and a bolt 36 which passes through and is secured to a center block 35 (see FIG. 3 also) mounted on plates 24 and 25 at a right angle to slot 28. Bolt 36 also passes through swivel 32A to provide the mounting of head 15 on universal coupling 32.

Fluid manifolds 33 and 34 are connected to a source of water 33A and by suitable piping 33B (illustrated partially in FIGS. 6 and 10) to a number of water jets 34A (see FIG. 9). and water pipes 29 serve to provide additional fluid coupling for each of the transducers of inspection head and a bearing surface on which the transducers may float because of their resilient mounting, to be described.

Referring now to FIG. 2A. an enlarged view of weld W is shown with the root and bead areas shown. Also, as illustrated by the shaded areas Z and Z the boundary zones of the weld are defined as the zone adjacent the ID. and OD. boundaries between the weld and adjacent plate. The heart of the weld is labled as H. An important feature of this invention is that specific inspection of each of the ID. and OD. boundary zones Z and 2 is provided by shear wave inspection simultaneously with inspection of the heart H of the weld and the plate adjacent the weld by longitudinal wave inspection. As used in the present application, longitudinal shear wave inspection refers to the generation and detection of echo signals from ultrasonic waves directed from the transducers down into and through the thickness of the weld or adjacent plates,

and travel in the direction ofpropagation. Also, as used 7 herein, transverse or shear wave inspection refers to the generation and detection of echo signals from ultrasonic waves travelling transverse to the direction of propagation and which lag behind the longitudinal wave. Since it is difficult to either longitudinally or transversely inspect all of a weld and its adjacent plate, the combinations of these type of ultrasonic inspection provides the required complete and overlapping inspection.

Inspection head straddles weld W so that it projects into groove 28 and as head 15 moves along the weld it may be inspected by the plurality of transducers mounted on head 15. In the embodiment illustrated in FIGS. 3 and 9 a first longitudinal wave transducers 40 is mounted in groove 28 so that it moves along and adjacent to the heart H of weld W as shown in FIG. 11. The face of transducer 40 towards weld W is curved to substantially correspond with the 'curvature of the weld, and a single housing may include both the transmit and receive cyrstals as represented by the letters T and R in FIGS. 9 and 11. Also, inspection head 15 includes a plurality of shear wave transducers 41A, 41B and 42A and 42B mounted on plate 24, and 43A, 43B and 44A and 44B mounted on plate 25. These transducers are mounted in pairs of transducers with a receiving and transmitting transducer in each pair, and each pair of the shear wave transducers inspects one of the OD. or ID. boundary zones Z or Z of weld W. In the example illustrated, transducer pair 41A and 418 (with transducer 41A being a receive transducer and transducer 418 being a transmit transducer) are mounted on plate 24 so that transducer 41B sends a shear wave pulse into the plate adjacent weld W which propagates through the plate at an angle of about 45 to pass through the boundary zone 2 on plate 24 side of weld W, and transducer 41A receives, upon occurence of a defect, an echo signal that returns from this boundary zone at about a 45 angle. Transducer pair 42A and 428 (with transducer 42A being a receiving transducer and 448 being a transmitting transducer) are mounted on plate 24 so that transducer 428 sends a shear wave pulse into the plate adjacent weld W on an angle of about 45 to pass through the boundary zone Z on plate 24 side of weld W, and transducer 42A receives an echo signal that returns from this boundary zone at about a 45 angle. Transducer pairs 43A and 43B, and 44A and 44B are arranged on plate 25 in the same manner (except that it is preferred that the transmitting transducers 43A and 44A be opposite receiving transducers 41A and 42A) to inspect boundary zones Z0 and Zm 0n the plate 25 side of weld W with a shear wavepulse of about a 45 propagation angle through the plate adjacent weld W.

The relation of the shear wave transducers described is illustrated in an exaggerated scale in FIG. 11 with only the transmitting transducers shown since the corresponding receiving transducers would be in line with its respective transmitting transducer. The desired propagation angle of about is provided by the angles at which each of the transducer crystals X are mounted in the transducer, and the type of acoustical coupling used in the transducer. By this arrangement the shear wave transducers are mounted so that their respective beams are focused or aligned to encounter one of the boundary zones of the weld, and the use of spread beam for inspecting these roots is avoided. One way of setting or focusing the shear wave transducers is to provide a test standard (the same size as welds to be inspected) with a known defect at the center of each boundary zone (generally a crack between the weld and adjacent plate) and to adjust the position of each of the shear wave transducers (as to be described) on plates 24 and 25 until the echo received for each re' spective crack by the respective shear wave transducer is peaked.

In an embodiment of this invention actually constructed and tested, the transmitting crystals X in transducers 41B, 42B, 43A, and 44A are mounted on a plexiglass coupling block B (see FIG. 11) so that shear wave ultrasonic signals from the crystals will strike the plate of pipe P at an angle of about 36 and propagate through the plate at about a 45 angle. An actual test, satisfactory sensitivity with steel pipe was provided when the shear wave propagation angle was from about 40 to with peak at about 44. Of course, these figures will vary slightly depending on the type of steel used in pipe P, temperature, and the frequency of the inspection waves. When the shear wave transmitting transducers are pulsed, a relatively fast longitudinal or surface wave pulse having maximum sensitivity along the wall of the pipe adjacent the tranducer (i.e., 0 entry angle) will be provided followed by slower shear wave pulses at the desired about 45 propagation.

In order to insure that the respective shear wave pulses pass through the weld root to be inspected, it is preferred that each of the shear wave transducers be mounted so that their lateral distance from the weld can be adjusted. As shown in FIG. 9, slots 248 can be provided in plate 24, and slots 25B ca be provided in plate 25 so that the shear wave transducers 41A, 41B, 42A and 42B can be mounted in moved back and forth in slots 24B, and transducers 43A, 43B, 44A, and 448 can be mounted in and slid back and forth in slots 258. For this purpose, each of the transducers can be mounted on flat plastic or aluminum plates 41C (shown in dotted lines in FIG. 9) which are in turn mounted by screws that pass through elongated slots 41D on each side of slots 24B and 253. As shown in FIG. 9, theID. boundary zone transducers 42A. 4213, 44A and 448 would be mounted at one lateral distance from weld W, and the OD. transducers 41A, 41B, 43A and 438 at another lateral distance from weld W. As noted, these positions can be set by placing inspection head over a weld substantially the same size as the welds to be inspected having known defects at the roots and adjusting for maximum signal strength. By this arrangement one inspection head 15 can be used to accommodate a wide range of wall thicknesses and weld bead widths.

Also, in order to inspect the plate of pipe P adjacent weld W. a longitudinal wave transducer 45 is mounted on plate 24 adjacent groove 28 on one side, and a second longitudinal wave transducer 46 is mounted on plate 25 adjacent to and on the other side of groove 28. Each of transducers 45 and 46 preferably includes a receiving and transmitting transducer in a single housing and provides for longitudinal wave inspection of the plate on either side of and adjacent to weld W for cracks or deviations from a normal weld thickness.

The details of mounting the transducers described in head may take many forms. However, whether head 15 or the specific transducers described takes the form of the example given or different forms, it is preferred that they be mounted in their respective mounting, such as in plates 24 and 25, with a sufficient clearance C between the transducers and adjacent plate 24 or 25 to permit canting of the transducer in response to irregularities in the surface being inspected, and that each transducer be resiliently mounting such as by a spring S (illustrated schematically in H0. 10) to permit the transducer to ride against the surface it inspects (with a suitable fluid coupling injected between the surface and the face of the transducer) against the bias of the spring and to yield and cant when a surface irregularity is encountered. Also, if the fluid bearing is provided with sufficient force, the transducer can ride on a layer of fluid off the surface being inspected.

For example. FIG. 10 illustrates the preferrred form of mounting of transducer 40. Transducer 40 is mounted on a cylindrical housing 40A open at one end and closed on the other end and its face F is urged out ofthe open end ofthe housing under the force ofspring 5 between the closed end of housing 40A and the shell of transducer 40. As shown, a small clearance C is provided between the shell of transducer 40 and the edge of 408 at the open end of housing 40A, and a shoulder 40C is provided on transducer 40 which abuts against edge 408 to provide a stop preventing transducer 40 from coming out of housing 40A. Housing 40A may be mounted in a circular opening in a plate 45L mounted on end plate 26, and the size of the circular opening in plate 45L may be adjustable to permit housing 40A to slide back and forth for setting the position of transducer 40 on weld W, and to permit transducer 40 to ride on a cushion of coupling fluid of substantially constant thickness (generally water) along the surface of weld W.

Referring now to FlGS. 12-18, the system of this invention and a preferred form of electronic pulsing and signal processing and readout electronic utilized with this system are shown. In FIG. 12, the ultrasonic inspection transducers are arranged about an imaginary weld W substantially as they are arranged on inspection head 15. A dual avalanche pulser 47 is provided having two output signals E and E and the transmitting transducers of each of the shear transducers 41B, 4213, 43A, and 44A are connected to output E The transmitting crystals ofthe longitudinal wave transducers 40, 45 and 46 are connected to output E of pulser 47. Pulser 47 also provides sync pulses E and E55 as hereinafter described. The receiving crystals of longitudinal wave transducers 45 and 46 are each respectively connected to time base measurement circuits 48A and 488 (to be described) and the outputs ofcircuits 48A and 48B are combined in a summing circuit 49 to provide an output signal E, which is proportional to the smallest (or largest) of the signals from circuits 48A and 488 to represent the thinnest of the plates on each side of weld W inspected by transducers 45 and 46, or a defect in one of the plates. Since this plate is generally uniform, signal E will generally be a substantially constat value until a defect such as a thin wall or lamination in the plate shows up in one of the plates adjacent weld W. The output E of circuit 49 is connected to an output of one channel of a chart recorder 50 having a chart 50a to provide a trace 5] in responce to the value of signal E and indicating the condition of the plate on either side of and adjacent weld W.

The receiving crystal of longitudinal wave transducer 40 is also connected to a time base measurement circuit 52 and its output signal E proportional to the thickness of the weld or to a defect in the weld, is connected to the input of another separate channel of recorder 50 to provide another distinctive trace 53 indicating the condition of weld W through its heart.

FIG. 13 illustrates a preferred form of time base measurement circuit for circuits 48A, 48B and 52 (the latter being shown in FIG. 13). The details of a similar circuit are set out in a co-pending patent application of Jerry Jackson, Ser. No. 117,663, Feb. 22, 1971, entitled "Time Base Measurement Circuit, and assigned to the applicant of this application (now US. Pat. No. 3,783,679). Circuit 52 includes a pre-amp 54 connected between the receiver crystal of transducer 40 and a differential comparator circuit 55 which functions to provide an output when an echo signal of sufficient magnitude is detected and crosses zero. By this method, as explained in the referenced patent application. the echo ai iyal ti rn e is de pen d e rt t on a phase con; ditio n of the echo signal instead of an amplitude..con d i- 1161, except that the amplitude of the echo signals must exceed the threshold level of circuit 55. The output of circuit 55 is conducted to start-stop circuit 56 which may be a Schmidt trigger that changes state to signal the receipt of the echo signal by transducer 40. The start-stop circuit 56 is initially turned on by receipt of a pulse from a block time generator 57 which may be a monostable multivibrator that responds to the sync pulse E, to provide a delayed start pulse for triggering circuit 56. The period of delay is set to be equal to the transit time of the main bang and echo pulses through the transducer coupling medium so that the time period between switching states of circuit 56 is proportional to nly the travel time of the transmitted and echo pulses iglthe object being inspected. The change in output of circuit 56 may be used to drive a digital to analog converter 58 to provide an analog output signal E proportional to the time duration between the arrival of the start and stop signals to circuit 58, and thus the time of arrival of the echo signal after the pulsing of the transducer.

Referring again to FIG, 12. the receiving transducers 41A, 42A, 43B and 44B of the shear wave transducers are connected through amplifier and detection circuits 59 (which provide an output when a certain input signal level is exceeded which is generally set just above the grain noise of pipe P) and switches 60 to a circuit 61 which provides an output signal E in response to the receipt of an echo signal atone of the shear wave receiving transducers. Unlike the longitudinal wave transducers, the shear wave receiving transducers generally do not receive an echo signal of sufficient level back from the specific weld boundary Zone being inspected to cause the detector 59 to provide an output unless a crack or other defect is present in the bound- 11 ary zone. Also, blanking signals are provided to circuit 61, has hereinafter described to cut it off except during the time that a true echo is likely to be received, if present. Thus, the output E of circuit 61, which drives a third separate channel of recorder 50 to provide a trace 62, is generally zero and trace 62 may be a straight line at a zero level until a defect is detected in one of the weld boundary zones.

As noted, the shear wave readout provides an indicatin with pulse duration proportional to the size of the defect (other than zero or no trace) only when one of the shear wave receiving transducers receives an echo signal back from one of the boundary zones that the about 45 focused beam is inspecting. This invention further includes two features which help insure that these rceiving transducers will respond to only the correct echo signal (if present). First by the mounting arrangement ofthe shear wave transducers shown in FIG. 9 where the receiving transducers 41A, 42A are directly opposite receiving transducers 43B and 448, the transmitted pulses from the transducers are less likely to be coupled into the receiving transducer on the opposite side. Second, as shown in FIGS. 14 and 15, inhibit or blanking pulses are provided by pulser 47 which inhibits the operation of the shear wave detector circuit 61 during a time period corresponding to the generation of the pulses for driving the longitudinal wave and shear wave transmitting transducers,and for a short period thereafter, but prior to the expected arrival time of a true echo pulse at one ofreceiving transducers 41A, 42A, 43B and 44B. Pulser 47 includes a clock 70 which may be an unijunction relaxation oscillator for providing periodic pulses (line A in FIG. 15) for example, at a repetition rate of 250 u see. The output ofclock 70 is conducted to a flip-flop 71 which provides two square wave outputs B and C l80 out ot phase with each other in response to pulses A. The two outputs B and C of flip'flop 71 are conducted to emitter followers 72A and 72B and then to unijunction pulse drivers 73A and 738 to respectively provide one ofalternate spike pulses D and F at 250 u sec. intervals, or 500 u sec. intervals for each of pulses D and F, to permit alternating, non-interfering shear wave and longitudinal wave inspection in synchronism and during the same inspection time. Pulse drivers 73A and 733 may be, for example, unijunction transistors responding to the leading edge of the output pulses ofthe emitter followers 72A and 728 to provide short duration spike pulses. Pulses D are conducted to a shear wave avalanche pulser 74A which, for example, may include an SCR connected through its power electrodes to shunt the transducer crystal voltage, to provide main bang pulses E, at 500 u sec. intervals for transmitting transducers 41B, 42B, and 43A and 44A. Pulses F are conducted to a longitudinal wave avalanche pulser 748 similar to pulser 74A to provide main bang pulses E for the longitudinal wave transmitting crystals of transducers 40, 45 and 46, at 500 u see. intervals between the intervals of pulses E,. Each of the drive signals E, to the shear wave transducers may be conducted through tuning coils L, and the drive signals to the longitudinal wave transducers may be provided through tuning coils L which may be tuned to peak the drive signals. The sync pulse output E of pulser 74A isalso conducted to a shear blank circuit 75 which may be a variable width monostable multivibrator providing, for example, a short duration (i.e. about 25 u see.) pulse G which is conducted to a blocking gate circuit 76, and the sync pulse E output of pulser 74B is conducted to a longitudinal wave blank circuit 77 which may also be a variable width monostable multivibrator providing, for example, a relatively long duration pulse H (i.e., about 250 u sec.) which is combined with pulse G (see FIG. 14) and conducted to gate 76. Gate 76 is thus closed during the time period of pulses G and H which would be during the time interval from a pulse E to pulse E, plus the short delay of pulse G. Gate 76 is connected in series with the shear wave signals so that during this period in which the gate is closed, which would be prior to arrival of the true echo signal at the shear wave receiving transducers, should one or more of the shear wave receiving transducers provide an output, this output would not pass through gate 76.

As shown in FIG. 14, shear wave detection circuit 61 includes a delay circuit 78 which delays the shear wave signals by a short amount-(i.e., 4 u see.) to insure that complete blocking of undesired signals occurs and that when the true shear echo signal arrives, gate 76 will be opened, and an amplifier79 conducting the shear wave echo signal to gate 76. The output of gate 76 may be conducted to an amplifier 80 for driving one channel of recorder 50 to provide trace 62. Since the shear signals are not analog, but their absence or presence is being detected, trace 62 could be a mark channel in which a Schmidt trigger driver (not shown) is provided to cause a mark to be made on a chart when the output of gate 76 is present in response to an echo signal. When a mark appears, switches 60 can be individually opened and closed by the operator to determine which of the shear wave receiving transducers received the echo, to locate the boundary zone in which a defect may be present.

FIGS. 16 and I7 illustrate the time relationship of the main bang signals (the ultrasonic pulse emitted by the transmitting crystals in response to the pulsers 74A and 748) from the various transmitting transducers and the echo signals received. Also, in FIG. 15, the generation of the main bang signals is illustrated. Since the higher the amplitude and the longer the duration of the main bang signal, the more well defined the echo signal will be, the avalanche pulsing scheme of FIG. 14 is designed to provide relatively large amplitude and long duration main bang signals. As shown in FIG. 16 (the curve of this figure applies to all of the transducer transmitting crystals), between main bang signals, the voltage level at the crystals is at a high level, for example 200 volts. When the SCR of pulsers 74A or 74B conducts to shunt the drive voltage, this voltage mementarily goes to zero and the crystal rings at its fundamental frequency (for example, 1.6 Hz for the shear wave transducers and 800 Hz for the longitudinal wave transducers). The period of ring determines the inspection period and the crystal voltages slowly return to the 200 level through their respective voltage paths. This sequence is repeated each 500 u see. for each of the transmitting crystals. By using a common drive oscillator for both the longitudinal wave and shear wave pulsers, synchronism is provided between the two types of inspection provided for (i.e., longitudinal and shear or transverse) and these two types of inspection can thus be carried on simultaneously (at alternate intervals) with the same inspection equipment.

FIG. 17 illustrates the alternate longitudinal wave and shear wave inspection, and with the notations thereon is self-explanatory. The longitudinal wave curve also illustrates the difference in arrival time of an echo due to a thin wall or a defect (the latter being in effect a thin wall) at, for example, one of the plate transducers, as opposed to normal wall. The shear wave curve illustrates receipt of a defect echo and the shear wave curve under normal conditions would not show the presence of an echo. Because the shear wave signals are considerably slower than the longitudinal wave signals, the arrival time of the shear wave echo is shown as 60 u sec. whereas the arrival time of the normal thickness longitudinal wave may be in the order of 12-15 u sec. after main bang. The arrival time of the echo representing thin plate wall would be something less than 12-15 sec.

FIG. 18 shows the type of chart readout that can be provided with the arrangement of transducers described (the example being taken from actual traces). The movement ofthe chart paper 50A can be synchronized with the movement of head 15 along weld W so that when a defect is encountered, its approximate location can be determined. For example, the carriage 10 may be moved at a rate of one foot per second and chart 59A can be moved at a rate of one inch per second. Since this movement is slow compared to the repetition rate of the ultrasonic inspection signals, a considerable amount of redundant inspection is provided for any area inspected so that the likelihood of missing a defect is small. Trace 5], representing the condition of the plate adjacent weld W, is shown as a straight line until an area 90 is reached at which time lamination 91 (FIG. 11) may be encountered, or a change in wall thickness adjacent the weld is encountered. A wall thickness change will generally be noted as a very gradual change whereas a lamination may be like a sharper change (the actual curve looking something like a square wave). Of course, in the case of lamination or other defect. a relative wall thickness measurement is provided with the echo time proportional to the depth of the defect. v

As noted, trace 51 will always represent the least wall thickness of the plate on either side of weld W, although in the event of loss of echo signal by one of the receiving crystals of transducers 4S and 46, indicating poor coupling or a small defect that does not permit an echo signal, the pin causing trace 51 will be driven against its limit. Trace 53 is an analog representation of the thickness of the weld bead, or indicating a defect, and the level 53 represents normal thickness, the level 53A represents a deviation from the normal thickness, and the level 5313 a defect, indicated by measuring the 'wall thickness from the inside wall, pipe P to the defect,

such as defect 92 in FIG. 11. If something prevents good acoustical coupling so that an echo does not return, or if a small defect is present which does not give an echo and prevents the usual echo coming from the bead, a level 53C may be provided where the recorder pin making trace 53 moves against the stop. If, upon checking for reoccurance of the signal, coupling appears not to be the problem, a defect can be assumed. For example, in FIG. 18 level 538 correlates in time with a mark on trace 62 (the slight lag in time being due to the fact that the transducer 40 sees the defect first) so that a defect such as a slag inclusion can be presumed. The same is true with mark 53D shown to correlate with a small mark on trace 62 and lamination 91 in the plate, indicating that the lamination extended right up to the weld.

Since the shear wave echos are only present when a defect is in or about the boundary zones of weld W (it being understood that even the sharply focused shear wave will inspect a small zone about the point where it is focused), a mark signal on trace 62 is generally not present, except as noted when a defect such as a crack 93 in FIG. 11 is present. Such a defect may result in mark 62A the width of which is proportional to the size of the defect. (This defect was not recorded by the other inspection transducers so that no time correlation is shown with traces 51 and 53.) Also, a meter or light (not shown) can be provided in each ofthe shear wave echo receiving channels to further aid in detecting which boundary zone provided an echo defect signal.

Thus, as can be readily appreciated by reference to FIG. 18, chart 50A, which can be calibrated in feet, can provide a simultaneous pictorial reprsentation of the condition of the bead of weld W, its roots, at the adjacent plate, and information concerning their location and size. Also, the speed of movement of chart 50A is relatively slow compared to the ultrasonic inspection pulse frequency so that overlapping is provided between inspected areas to insure that any point of the weld is adequately inspected. However, the overall speed of the system is such, with the arrangement of carriage 10 described, only a few minutes is required for inspecting the long seam weld on a standard 40 foot length of pipe.

Also, while a single event trace is disclosed herein for the shear wave outputs, and this is preferred because it permits easier interpretation of the chart by relatively unskilled persons, it would be possible with added recorder cost and complexity to provide a separate analog trace for each shear wave receiver output. This may be desirable where a person who is highly skilled in pipe inspection is interpreting the results. Also, the sensitivity of the system can be adjusted to suit the type of person interpreting the results. For example, ifhe is less skilled, then low sensitivity, so that only defects are recorded may be desired, but if he is of higher skill, he may wish to see smaller irregularities in the weld pattern which are not defects.

ln order to insure that carriage 10 stops automatically when it reaches the end of a pipe being inspected, and does not fall out of the pipe, a feeler arm may be pivotally mounted on the from head 15 to extend forward of the head, as shown in FlG. 1. Arm 100 may be biased towards the pipe wall by a spring (not shown) and a normally closed micro switch 101 may be mounted on its end so that when it is against the pipe it is open, and when the switch 101 is clear of the pipe wall, it will be closed. An electric brake mechanism may be mounted on one of the wheels 13a and operated by switch 101 so that when switch 101 is closed, the brake is activated. Also, if desired, more than one wheel 13a can be driven (by one or more motors) to aid in traction, particularly since the inside of the pipe will probably be wet.

Also, a suitable housing 103 may be provided on one end ofthe carriage 10 for the mounting of the drive and receiving electronics (except the recorder electronics) to reduce the number and length of lead lines to carriage 10f "From the foregoing, it will be seen that this invention is one well adapted to attain all of the ends and objects l hereinabove set forth, together with other advantages which are obvious and which are inherent to the apparatus.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims.

As many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

The invention having been described, what is claimed l. Ultrasonic apparatus for inspecting an elongated butt weld comprising, in combination: an inspection head adapted to be moved along and adjacent to the weld; a longitudinal wave ultrasonic transducer mounted on said inspection head and adapted to be positioned on said weld to move along its length for inspection through a substantial part of the heart of the weld; a plurality of shear wave ultrasonic transducers mountediifi said inspection head to be pomn ed on each side of the weld to provide for inspection of the boundary zone of the weld, and means on the inspection head to restrain movement thereof to be longitudinally along the elongated weld without any substantial movement laterally of the weld.

2. The apparatus of claim 1 further including a pair of third ultrasonic transducers mounted on said inspection head for inspecting plate adjacent to and on each side of said weld.

3. The apparatus of claim 2 wherein said third transducers are longitudinal wave ultrasonic transducers.

4. The apparatus of claim 1 wherein said shear wave transducers are provided for inspecting each boundary zone ofthe weld and being mounted on said inspection head to be on one side of the weld, one of each pairs of transducers providing an ultrasonic impulse and the other of each pair of transducers receiving ultrasonic echo signals from said weld.

5. The apparatus of claim 4 including means for mounting each of said shear wave transducers so that the lateral distance of each transducers from weld being inspected may be adjusted, whereby the transmitting transducer of each pair may direct an ultrasonic pulse substantially into only one of the boundary zones of the weld, and the receiving transducer of each pair receives ultrasonic echoes from its respective only one boundary zone of the weld.

6. The apparatus of claim 4 wherein such a pair of shear wave transducers is mounted on opposite sides of said inspection head to be on opposite sides of said weld for inspecting the boundary zones on either side of the weld, and wherein the receiving transducers of a first pair of transducers on one side ofsaid head is opposed to and in line with the transmitting transducer of a second pair of such transducers on the other side of said head, and the transmtting transducer of said first pair of transducers is opposed to and in line with the receiving transducers of said second pair of transducers.

7. The apparatus ol'eluim 4 wherein said transmitting shear wave transducer includes a crystal mounted therein to provide an ultrasonic pulse at an angle with respect to the plate surface adjacent a weld to be inspected such that the pulse propagates through said plate on a path at about a -50 angle with respect to surface of the plate, and said receiving shear wave transducer includes a crystal mounted therein for primarily detecting and responding to ultrasonic signals travelling through said plate on such a path.

8. The apparatus of claim 7 wherein said crystal is mounted so that said path is about 9. An ultrasonic inspection system for inspecting an elongated butt weld comprising, in combination: electronic drive means for providing periodic ultrasonic drive pulses, a first ultrasonic transducer connected to said drive means and responding to such drive pulses for inspecting a substantial portion of the thickness of such a bead; first tim basgm easurement means connected to said first transducer fofi'espoiiding to echo ultrasonic pulses received by said transducer to provide a first distinctive output signal responsive to the condition of said weld; a plurality of second ultrasonic transducers connected to said drive means and responding to such drive pulses for inspecting the boundary zones of such a weld; and electronic signal detecting means connected to said second ultrasonic transducer for providing a second distinctive output signal in response to an abnormal condition at at least one of said boundary zones, means mounting said transducers to be moved longitudinally along the weld without any substantial movement laterally of theweld, and a plurality of third ultrasonic transducers connected to said drive means and responding to such drive pulse for inspecting plate adjacent to and on each side of the weld, and second time base measurement means connected to each of said third transducers for responding to ultrasonic echo signals therefrom to provide a third distinctive output signal responsive to the condition of said plate.

10. The apparatus ofclaim 9 further including a chart recotdetjayinga first channel responsive to said first distinctive output signal to provide a first distinctive trace, a second channel responsive to said second distinctive output signal to provide a second distinctive trace, and a third channel responsive to said third distinctive output signal to provide a third distinctive trace whereby simultaneous inspection of said first, second and third traces can provide distinctive and composite indications of the condition of the heart ofthe weld, the condition of the boundary zones of the weld, and the condition of the plate adjacent the weld.

11. The system of claim 9 wherein the weld to be inspected is the long seam weld of racked pipe, and further including a carrier adapted to be inserted i n a n,d

m ovedalong the length such pipfand an inspection lie'ad re sili'entlyiiiounte d on aid carrier to move about and along said weld, and wherein said first, second, and third ultrasonic transducers are mounted on said inspection head.

12. Ultrasonic apparatus for inspecting longitudinal butt welds in a pipe comprising, in combination: a c ar rier adapted to be moved along the length of such'a pipe; an inspection head resiliently mounted on said carrier aii dadapted to be moved along the weld to be inspected; means for guiding said head on the weld in a manner tcT'cause the transducer to move longitudinally along the weld without any substantial movement laterally of the weld; means for urging said head against the inside wall of a pipe being inspected; a first ultrasonic transducer mounted on said inspection head and adapted to be positioned over said weld to move along its length for inspection through a substantlal part of the weld head; a plurality of second ultrasonic transducers mounted on said inspection head to be positioned and to provide for inspection of a root of the weld; and a pair of third ultrasonic transducers mounted on said inspection head for inspecting plate adjacent to and on each side of said weld.

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1. Ultrasonic apparatus for inspecting an elongated butt weld comprising, in combination: an inspection head adapted to be moved along and adjacent to the weld; a longitudinal wave ultrasonic transducer mounted on said inspection head and adapted to be positioned on said weld to move along its length for inspection through a substantial part of the heart of the weld; a plurality of shear wave ultrasonic transducers mounted on said inspection head to be positioned on each side of the weld to provide for inspection of the boundary zone of the weld, and means on the inspection head to restrain movement thereof to be longitudinally along the elongated weld without any substantial movement laterally of the weld.
 2. The apparatus of claim 1 further including a pair of third ultrasonic transducers mounted on said inspection head for inspecting plate adjacent to and on each side of said weld.
 3. The apparatus of claim 2 wherein said third transducers are longitudinal wave ultrasonic transducers.
 4. The apparatus of claim 1 wherein said shear wave transducers are provided for inspecting each boundary zone of the weld and being mounted on said inspection head to be on one side of the weld, one of each pairs of transducers providing an ultrasonic impulse and the other of each pair of transducers receiving ultrasonic echo signals from said weld.
 5. The apparatus of claim 4 including means for mounting each of said shear wave transducers so that the lateral distance of each transducers from weld being inspected may be adjusted, whereby the transmitting transducer of each pair may direct an ultrasonic pulse substantially into only one of the boundary zones of the weld, and the receiving transducer of each pair receives ultrasonic echoes from its respective only one boundary zone of the weld.
 6. The apparatus of claim 4 wherein such a pair of shear wave transducers is mounted on opposite sides of said inspection head to be on opposite sides of said weld for inspecting the boundary zones on either side of the weld, and wherein the receiving transducers of a first pair of transducers on one side of said head is opposed to and in line with the transmitting transducer of a second pair of such transducers on the other side of said head, and the transmtting transducer of said first pair of transducers is opposed to and in line with the receiving transducers of said second pair of transducers.
 7. The apparatus of claim 4 wherein said transmitting shear wave transducer includes a crystal mounted therein to provide an ultrasonic pulse at an angle with respect to the plate surface adjacent a weld to be inspected such that the pulse propagates through said plate on a path at about a 40*-50* angle with respect to surface of the plate, and said receiving shear wave transducer includes a crystal mounted therein for primarily detecting and responding to ultrasonic signals travelling through said plate on such a path.
 8. The apparatus of claim 7 wherein said crystal is mounted so that said path is about 45*.
 9. An ultrasonic inspection system for inspecting an elongated butt weld comprising, in combination: electronic drive means for providing periodic ultrasonic drive pulses, a first ultrasonic transducer connected to said drive means and responding to such drive pulses for inspecting a substantial portion of the thickness of such a bead; first time base measurement means connected to said first transducer for responding to echo ultrasonic pulses received by said transducer to provide a first distinctive output signal responsive to the condition of said weld; a plurality of second ultrasonic transducers connected to said drive means and responding to such drive pulses for inspecting thE boundary zones of such a weld; and electronic signal detecting means connected to said second ultrasonic transducer for providing a second distinctive output signal in response to an abnormal condition at at least one of said boundary zones, means mounting said transducers to be moved longitudinally along the weld without any substantial movement laterally of the weld, and a plurality of third ultrasonic transducers connected to said drive means and responding to such drive pulse for inspecting plate adjacent to and on each side of the weld, and second time base measurement means connected to each of said third transducers for responding to ultrasonic echo signals therefrom to provide a third distinctive output signal responsive to the condition of said plate.
 10. The apparatus of claim 9 further including a chart recorder having a first channel responsive to said first distinctive output signal to provide a first distinctive trace, a second channel responsive to said second distinctive output signal to provide a second distinctive trace, and a third channel responsive to said third distinctive output signal to provide a third distinctive trace whereby simultaneous inspection of said first, second and third traces can provide distinctive and composite indications of the condition of the heart of the weld, the condition of the boundary zones of the weld, and the condition of the plate adjacent the weld.
 11. The system of claim 9 wherein the weld to be inspected is the long seam weld of racked pipe, and further including a carrier adapted to be inserted in and moved along the length of such pipe, and an inspection head resiliently mounted on aid carrier to move about and along said weld, and wherein said first, second, and third ultrasonic transducers are mounted on said inspection head.
 12. Ultrasonic apparatus for inspecting longitudinal butt welds in a pipe comprising, in combination: a carrier adapted to be moved along the length of such a pipe; an inspection head resiliently mounted on said carrier and adapted to be moved along the weld to be inspected; means for guiding said head on the weld in a manner to cause the transducer to move longitudinally along the weld without any substantial movement laterally of the weld; means for urging said head against the inside wall of a pipe being inspected; a first ultrasonic transducer mounted on said inspection head and adapted to be positioned over said weld to move along its length for inspection through a substantial part of the weld bead; a plurality of second ultrasonic transducers mounted on said inspection head to be positioned and to provide for inspection of a root of the weld; and a pair of third ultrasonic transducers mounted on said inspection head for inspecting plate adjacent to and on each side of said weld. 